The application is designed to evaluate the role of the IL-2/IL-2R pathway, found to be ubiquitously expressed in malignant and normal tissues, in growth regulation of oral squamous cell carcinoma (OSCC) cells. The studies completed in the last three years indicate that IL-2 is produced, but not secreted, at levels detectable in ELISA by human OSCC and that it functions as a growth hormone and apoptosis protection factor in tumor cells. These cells also express functional IL-2R. Exogenous IL-2 binding at nM concentrations to its receptor inhibits growth of OSCC cell lines by inducing cell cycle arrest in G0/G1. The mechanisms responsible for growth-promoting signals mediated by endogenous IL-2 vs. negative growth signals delivered by exogenous IL-2 will be investigated in vitro and in vivo, using both OSCC cell lines and xenograft model of OSCC immunosuppressed BALB/c nude mice established in the Prinicpal Investigator's laboratory. They hypothesis to be tested is that endogenous IL-2 acts as growth-promoting factor in OSCC cells by down- regulating expression of CDK cell cycle inhibitors, while exogenous IL-2 interferes with growth by disrupting this essential endogenous pathway. Expression, activity and transcriptional regulation of Cyclins, CDKs and CDK inhibitors and Rb protein phosphorylation levels in OSCC cells treated with antisense IL-2 or antisense IL-2Rbeta and in untreated control cells will be evaluated and related to growth in vivo in OSCC- xenografted nude mice. Mechanisms of IL-2 mediated protection of tumor cells from apoptosis possibly by regulation of the state of Rb protein phosphorylation will be probed. Intracellular pathways of IL-2 mediated protection of tumor cells from apoptosis possibly by regulation of the stat of Rb protein phosphorylation will be probed. Intracellular pathways of IL-2 and IL-2r processing, localization and trafficking in tumor cells will be studied by confocal and immunogold electron microscopy to determine whether exogenous vs. endogenous IL-2 pathways operate in distinct cellular compartments. Understanding of the regulatory role of the IL-2/IL-2R pathway in tumor cells provides opportunities for novel therapeutic interventions in OSCC based not only on arrest of tumor growth by exogenous IL-2 but also on the use of pharmacologic and/or biologic agents known to be able to disrupt the IL- 2 pathway.